Abstract

Unlike other thin film deposition techniques, close spaced sublimation (CSS) requires a short source-substrate distance. The kind of source used in this technique strongly affects the control of the deposition parameters, especially the deposition rate. When depositing CdTe thin films by CSS, the most common CdTe sources are: single-crystal or polycrystalline wafers, powders, pellets or pieces, a thick CdTe film deposited onto glass or molybdenum substrate (CdTe source-plate) and a sintered CdTe powder. In this work, CdTe thin films were deposited by CSS technique from different CdTe sources: particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass). The largest deposition rate was achieved when a paste made of CdTe and propylene glycol was used as the source. CdTe source-plates led to lower rates, probably due to the poor heat transmission, caused by the introduction of the plate substrate. The results also showed that compacting the powder the deposition rate increases due to the better thermal contact between powder particles.

Highlights

  • Cadmium telluride (CdTe) has been shown to be the most promising polycrystalline thin film material for producing photovoltaic solar cells because of its high absorption coefficient (> 104 cm-1) and optimum bandgap (1.5 eV)

  • Different CdTe sources were used for depositing CdTe thin films by close spaced sublimation (CSS): particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass)

  • Different CdTe sources were used for depositing the films: particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass)

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Summary

Introduction

Cadmium telluride (CdTe) has been shown to be the most promising polycrystalline thin film material for producing photovoltaic solar cells because of its high absorption coefficient (> 104 cm-1) and optimum bandgap (1.5 eV). The most efficient CdTe solar cell reported so far is a 16.5% device[1], whose CdTe layer was deposited by close spaced sublimation (CSS) technique This technique involves the sublimation of CdTe from a source which is separated from the substrate by a small distance, usually, millimeters. It is an attractive process since it offers high depositions rates, it is able to produce films with larger grains than those deposited by other techniques and can be scaled up for manufacturing purposes. Different CdTe sources were used for depositing CdTe thin films by CSS: particles, powder, compact powder, a paste made of CdTe and propylene glycol and source-plates (CdTe/Mo and CdTe/glass). The influence of these sources on the deposition rate of the films was investigated

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